How do coral reefs form? What are coral reefs

Coral reefs are the largest and most magnificent living structures on our planet, the greatest reservoirs of biological formations. Although today, unfortunately, they are under the threat of extinction. Scientists have calculated that if immediate measures are not taken to correct the situation, then we risk losing up to 70% of all coral reefs by 2050.

Let's hope that people still manage to save our oceans, including coral reefs, in the form that they are today, and our descendants will be able to admire their splendor not only from pictures in books, but also live.

We invite you to take a look at our selection of coral reefs, which are considered the most beautiful and fantastic on Earth.

Coral reefs of the Red Sea

The Red Sea is home to over 260 different types of stony corals and over 1,100 species of fish. This sea is located between the Sahara and the Arabian deserts. The Red Sea coral reef is over 1200 miles long. Its age exceeds 5000 years. They began to emerge during the reign of the ancient Egyptian pharaohs.

Coral reefs Florida Keys

The shallow waters of the Florida Keys provided ideal conditions to create beautiful coral reefs. These corals were formed due to the warm tropical climate under the influence of waves. There is a lot of plankton here, which is necessary for the survival of various types of living creatures. Unfortunately, these reefs are on the verge of extinction and, according to some sources, by 2020 they may completely die.

Mesoamerican Barrier Reef

The Caribbean Sea is home to many varieties of fish and rare animals. It borders one of the largest and most beautiful coral reefs in the world. Its size is approximately 943 kilometers. This reef is also under threat from changes in sea levels and ocean chemistry.

For many years, in the area of ​​​​the Philippine Apo coral reef, there was an active fishery for catching all living things, including the use of incendiary substances. As a result, a third of the coral reef has completely disappeared. The Philippine government has decided to ban fishing in an area of ​​170 square miles off the coast of Mindoro Island. Today Apo Reef is national park and protected area.

Andros in the Bahamas is considered one of the longest barrier reefs in the world (its length is more than 140 miles). Divers have the opportunity to explore many interesting areas within these reefs. Andros Island, near which this reef is located, is located along the edge of the crevice of the ocean, which is called the Tongue of the Ocean.

Maldives Chagos-Lakshadvil Atolls

This structure is a chain of coral reefs that is 280 km long. These reefs are located along the coast of Belize, approximately 300 meters from the coast in the northern part and 40 kilometers in the southern limits of the country. The Belize Barrier Reef is part of the Mesoamerican Barrier Reef, which is one of the largest reefs in the world (2nd after the Great Barrier Reef).

The very name "Raja Ampat" means "4 kings". The four large islands of Batanta, Misuul, Salwati and Waigeo, which are connected to hundreds of smaller islands, surround these coral reefs. This Indonesian coral reef is rich in wildlife. There are more than 1,500 species of fish, about 700 species of molluscs and over 500 species of stony corals.

Barrier reef of New Caledonia

This is the third largest coral reef and is also considered one of the most magnificent in the world. It is here that the endangered dugong lives, and green turtles also lay their eggs. The place near the reef is famous for its clear waters. The lagoons of this barrier reef are included in the list of UNESCO World Heritage Sites.

This reef extends for approximately 130,000 square miles. This is more than the United Kingdom. The Great Barrier Reef is arguably the largest coral reef in the world. Moreover, it is even the largest object created naturally from living organisms. It is considered one of the seven world wonders.

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Coral reefs- these are huge rocky heaps formed by millions of tiny creatures - coral polyps. Reef-building coral polyps build protective skeletons for their soft bodies from limestone - calcium salts, which they extract from sea water. These shells are in the form of bowls, disks or boxes. Each colony grows and develops in a pattern as old polyps bud into new individuals. Old polyps gradually die off, leaving empty hard shells, and new polyps grow above them. This is how, centuries later, thousands of coral skeletons form bizarre reefs. Reef-building coral polyps build some of the toughest and most massive formations in the living world. But they themselves are very gentle creatures, able to survive only in warm, clean, well-warmed sea shallow water. This is partly because each polyp contains hundreds of microscopic creatures called dinoflagellates that need sunlight to grow and develop. Polyps provide their symbionts with shelter, minerals and other substances they need. Those, in turn, using solar energy, create food for themselves and share it with corals. Thus, coral polyps need sunlight to thrive.

Coral reefs- one of the richest, in terms of species diversity, corners on Earth. The front part of the reef descends stepwise into the sea, and it is in this part that the action of storms is most strongly felt. But on the other side of the reef, which has ledges and ridges, there is usually a shallow, calm area - a reef lagoon, protected from large waves. Cavities and crevices in the rocks of the reef serve as a refuge for a variety of fish, shrimps, worms, crabs and starfish, other animals, as well as algae.
Corals are very sensitive to environmental changes. Oil that enters the water from tankers pollutes sea water and destroys corals that serve as a food source for many animals. Another danger is wastewater from fields and forest clearings. They merge into rivers and then end up in the sea. Mud makes the water cloudy, and it does not allow sunlight to pass through, which is necessary for the protozoa with which the corals are in symbiosis. In addition, in many parts of the world, coral skeletons are recovered from the water to be sold to tourists. Such trade is destroying some reefs at an alarming rate.
Another natural enemy of corals is starfish, which eat polyps, especially in the Indian and Pacific Oceans. One of these predators can destroy 4.6 square meters of coral annually. On some reefs, the number of starfish has increased significantly, partly as part of the natural cycle, and partly due to human activities.

Coral reefs are second only to tropical forests in terms of richness and diversity of life forms. They are home to millions of different animal species, including a third (over 7,000) of all fish species.
Coral reefs form only in tropical or subtropical shallow waters, where the average annual temperature exceeds 20 degrees.
Corals are usually named after the shape of their colonies. This form is determined by how the polyps grow and bud off. The curves and folds of the coral-brain resemble in shape human brain.
Corals - gorgonians have a delicate lacy shape. The finger coral looks like a hand. There are many mushroom corals.
The Great Barrier Reef stretches over 2,000 km along the coast of northeastern Australia. It took millions of years for it to reach this size. The Great Barrier Reef is much larger than any structures created by living organisms (including humans!). 3,000 smaller reefs are now natural parks where corals and their habitats are protected.

A few centuries ago, when brave sailors plied the oceans on sailing fragile wooden boats, an encounter with an underwater reef did not bode well for travelers.


Today, coral reefs are the most attractive tourist attractions in many seaside resorts. Many people want to know what a reef is in the ocean, to see the splendor of the underwater kingdom with their own eyes.

What is a reef?

Word "reef", like many other nautical terms, is borrowed from the Dutch language, in which it means "edge" . This word in modern Russian has several meanings:

- a narrow rocky strip, hidden by water or slightly protruding above the sea surface, and extremely dangerous for ships sailing next to it;

- a sail device that allows you to quickly reduce its volume to control a sailing vessel, using special garters called reef seasons;

- a perennial colony of marine coral polyps, the dead skeletons of which have formed a dense limestone massif that serves as the basis for new corals and a habitat for other marine animals.

Currently the word "reef" usually used in the third sense, and with an adjective "coral".

Coral reef in the ocean

Do not be surprised at the ability of coral polyps to form whole rather big islands. There is nothing surprising in this, especially if we consider the biological productivity of these creatures. The growth rate of coral biomass remains unchanged throughout the year and is approximately 50-300 grams per day per square meter of reef. They form the basis of the ecosystem, in which, in addition to corals, almost all types of living creatures participate, from bacterioplankton to mammals.

Coral reefs occupy more than 600 thousand square kilometers on our planet, located mainly in the warm seas of Southeast Asia (about 45% of all reefs), the Atlantic (14%), the Indian Ocean (17%), the Pacific Ocean (18), as well as in the Red Sea (about 6%). The main habitat of corals is the shelf of large islands and continents warmed by the sun.


The largest reefs on the planet are the Great Barrier Reef (the length is more than 2 thousand kilometers, the total area is about 215 thousand square kilometers), the reef systems of Belize, the Fiji Islands, New Caledonia and Tulear not far from Madagascar.

Varieties of coral reefs

Depending on the shape, coral reefs are divided into the following types.

1. Barrier. A wide strip of reef stretches along the coastline, separated from the land by a fairly deep lagoon, the width of which can reach several tens of kilometers and a depth of 70 meters. The width of the reef itself ranges from hundreds of meters to several kilometers. The strip can be single, double and include reef rings.

2. Bordering. The reef runs along the coast and closely adjoins it or leaves a narrow lagoon no more than one or two meters deep between the flat (upper part) and the coast.

3. Key reef. A flat small reef is located in shallow water, and its leeward side was covered with sand until the formation of a spit or a small island.

4. Platform. A flat reef in the form of a small island protrudes from the water at low tide, and its flat, overgrown with algae, is partially covered with clastic rock and sand.

5. Coral jar. A mound of indeterminate shape, created by the activity of coral polyps, is all the time almost or completely hidden by water.

6. Atoll. An annular calcareous island forms on top of an underwater volcano. Its composition includes different types reefs - banks, islets, flat reefs and even small ones. There is at least one lagoon in the center, but most often there are several.

7. Linear. Reef rectilinear ridge 50-100 meters wide, consists of small reefs of all existing types. Even small atolls can be located on its edges, which are often filled with sand and calcareous debris.

How are reefs formed?

Research shows that most reefs that exist today are no more than 10,000 years old. They most likely formed during the rise in the level of the World Ocean, which was caused by the melting of ice after the end of the Great Ice Age and led to the formation of a vast one.

The well-heated water of the shallow shelf served as an excellent environment for the existence of coral polyps, around which a rich biocenosis soon developed. As the calcareous base grows, the edges of the reef break off during storms and are carried by waves to its flat, where they accumulate and compact. As a result, coral islands of a fairly large size are formed over millennia.


In addition, reefs often form on the tops of underwater volcanoes that have risen close to the sea surface as a result of tectonic activity in the earth's crust. This hypothesis of the origin of reefs was put forward by Charles Darwin. According to his theory, atolls go through three stages of development. Initially, corals form a colony on the edges of the top of the volcano, grow and form a fringing reef, which subsequently grows to the barrier stage and gradually becomes an atoll.

Coral is a structure made up of millions of very small marine animals called polyps. The polyp, which is tube-shaped, is only an inch long. At the end of this tube is a mouth surrounded by tentacles that bring sea creatures to it. The color of corals is very diverse, as well as their shapes and sizes. They have both an internal and an external skeleton. They can be soft or hard, black, smooth or prickly and other types. Some are like feathers, others are like fingers. The polyps are hollow and attach themselves to other polyps or to limestone rocks to form large structures. Almost all corals live together in groups called colonies. Very large colonies are called reefs. Polyps take calcium from seawater and turn it into limestone around their lower body. New polyps grow and the limestone structure gets bigger and bigger.

Corals live in oceans all over the world, but survive best in warm water. In tropical oceans, they form large structures called atolls. Atolls grow around old volcanoes and form ring-shaped islands. Coral polyps eat small marine animals such as jellyfish larvae. Some people need seaweed to survive. Corals can reproduce by budding. Small buds appear on the body of the polyp. They grow up and separate from their parents. Corals can also lay eggs that grow into new colonies. Some types of coral live for hundreds of years.

coral reef

A coral reef is an underwater mountain formed by coral skeletons. Reefs are also made up of other living things such as seaweed or shellfish. The coral reef has vibrant colors and can grow for hundreds of years without being destroyed by the ocean. Location of coral reefs around the world.

Reef types:

• Reef line - located near the coast line they are usually the youngest reef forms
• Barrier reefs are located farther from the coast they form a wall between shallow water near the coast and the open sea some barrier reefs are very large The longest - 2 thousand kilometers long The Great Barrier Reef on the east coast of Australia
• Atolls are ring-shaped reefs. They form when an old volcano erupts and sinks into the sea.
  Most reefs need warm water to survive They grow best in water that is at least between 16 and 20 degrees. Reefs also need enough sunlight to feed. Coral reefs can also be found in the warm ocean waters of the Pacific and Indian Oceans as well as in the Caribbean Sea and the east coast of the central part. South America They usually grow very slowly, no more than 10 cm per year. They can be found near the surface where they get enough sunlight.

Life on coral reefs

A coral reef can have thousands of different types of corals and other organisms. This would be a record if not for the rainforests, which can contain even more different organisms. Therefore, coral reefs are called tropical forests of the sea. Many fish species live near coral reefs. Their bodies have the ability to change, which makes it possible for them to live and find food in this area. In addition, coral reefs are home to crabs, lobsters, octopuses, starfish and other invertebrates.

Significance of corals and coral reefs:

1. Corals remove and recycle carbon dioxide, a gas that is responsible for the greenhouse effect.
2. Reefs protect islands and continents from waves and storms and allow other species to thrive in the shallow waters near the coast.
3. A coral reef is a complex ecosystem with many different types of organisms. Without reefs, they would die.
4. Coral skeletons are used as substances for bones and other parts of our body.
5. Coral reefs are living laboratories for scientists and students.
6. The reefs attract millions of tourists every year.
7. People make jewelry made from coral reefs.

Major threats to coral reefs:

Coral reefs are an attractive sight for tourists and an undesirable phenomenon for passing ships. Many wish to visit resorts in the basins of the Pacific and Indian Oceans - the places where they are concentrated.

Definition

Several meanings of the reef:

• pile of stones. Rocky, sandy, coral formations due to the elevation of the bottom and erosion of the coast. Heaps of remains of mollusks, algae and some reef-building organisms;
• a rocky strip hidden or protruding slightly above the water level;
• coral polyps as a perennial colony that serves as a habitat for various animals and the basis for new growths of the next generation;
• in another meaning: a reef is a device for reducing the volume of a sail in case of a strong wind.

Reefs are formed due to the deposition of sand, the erosion of certain rocks, and other processes. They are formed as a result of the growth of coral polyps and combination with calcareous algae. Coral reefs are shallow, wave-resistant structures built by the release of lime by marine organisms. Polyp formations are located on underlying bases that differ in chemical properties.

Classification

Barrier reefs are located near islands far from the coast and can be separated from it by a strait. Coral - the most common. The most voluminous is the Great Barrier Reef of Australia, which stretches for 1600 km along the coast.

Fringing - have the form of a platform like a terrace, which starts from the coast and extends deep into the ocean. Often they end with a raised edge. They can be found along exposed or stable coastlines.

Atolls are ring-shaped structures, sometimes with several ring breaks, with a lagoon in shallow water, in the form of giant rings. They can be mistaken for islands, and only by paying attention to the lack of land inside, you can understand that these are reefs.

Transitional types of stony formations are characterized by similar features with several corals. Some islands are distinguished by the presence of volcanic rocks in the center of the ring. In the case of others, if you look at the submerged platform from below, it may turn out that this is an atoll-type reef or an underwater island.

coral species

There are hundreds of varieties of corals that differ in color, shape, size. They can be round and folded, tall, fan-shaped, reminiscent of plants. They are called tropical marine forests, as they are home to over 4,000 species of fish, 700 species of polyps and many thousands of different living creatures. Corals belong to the species of stingers: jellyfish, anemones, Portuguese man-of-war.

"Brains" are hermaphrodites, they produce female and male cells, and their reproduction occurs as a result of mass spawning, while in other species this phenomenon is observed once a year.

There are two known ways of feeding corals. The first - with the help of stinging tentacles, catching small fish, plankton; the second is a symbiotic relationship in which algae exist within the polyp and, through the process of photosynthesis, take food for themselves and for the polyp, and receive carbon dioxide and shelter. Most corals do not have their own shade, and zooxanthellae color them in certain colors.

Conditions of existence

Corals are the most important component of the inner life of the ocean, depending on which its inhabitants live and develop. They provide a person with an economic benefit equivalent to 30 billion dollars a year through fishing, tourism, and food.

The habitat of corals is shallow water, warmed up to an acceptable temperature (22-27 degrees), a sufficient amount of sunlight so that algae can synthesize nutrients and deliver them to polyps. The Australian Reef gradually disappears closer to Antarctica. Water level, salt percentage, temperature - all these conditions must correspond to the optimal indicators for the development of polyps.

Currently, corals are under the threat of ocean acidification, which is possible through the penetration of CO 2 from the atmosphere. Under the influence of carbon dioxide obtained during the combustion of fuel substances, they stop growing.

With the global warming of ocean waters, corals reject zooxanthellae algae, giving them a peculiar brightness. In the absence of vegetation, their interaction with corals and many living organisms ceases. It is known that such reefs become colorless over time, as a result of which they die.

The crown of thorns starfish is a known reef pest that arrived from the South Pacific: it eats about a meter of the ecosystem every week. To combat it, chemical methods are excluded so as not to harm other inhabitants, so the capture of an aquatic inhabitant remains optimal.

The structure of polyps, formed over thousands of years, can be destroyed in a few minutes if fish are caught by explosive methods, trawlers or using cyanides.

What is a reef in terms of stability? This is an ecosystem that grows and collapses at the same time: fish and animals feed on it, acids corrode it, and wash out the current. The visible part of the corals is constantly changing and decomposes into grains of sand over time. But even in adverse conditions, the reef grows up to 30 cm per year.

australian reef

The origin of coral reefs began about 25 million years ago with the displacement of the Australian plate of the lithosphere. Their total world area is equal to 27 million km2. About 3,000 rocky structures and 900 offshore islands make up Australia's Great Barrier Reef, one of the world's largest living organisms. The park, located under water, covers an area of ​​more than 344,000 km2.

To date, only ten percent have been studied. What a reef is is known, but the features of its coexistence with all the inhabitants and components are being studied. Eyewitnesses claim that no office equipment is able to display the natural beauty and silence of the Australian reserve.

If you dive below ten meters deep, you can see the glow of corals and admire the number of their shades: red, green, purple, black, yellow, brown, white. The reef is about 400,000 years old, and its growth has accelerated with rising ocean levels. New sites are located above the old ones at a depth of about twenty meters. Thousands of generations of its colonies will change before the reef takes on new shapes and sizes.

Discoverer

In 1770, navigator James Cook, sailing over a rocky strip of coral, unexpectedly had a chance to learn what reefs were when their edges stuck into the ship and pierced its hull. The crew had to dump tons of cargo, including a heavy firearm, to lighten the ship and bring it to the shallows to eliminate numerous holes. The cannons, raised from the bottom by tourists a century later, have become museum pieces, and one of them was left on Green Island.

About five hundred ships were wrecked in the area of ​​the reef, some researchers tried to map it. In 1970, an oil tanker sank to the bottom in this place. Torres Straiters and Australian Aborigines fished here, so Cook wasn't the only one who discovered the reef.

inhabitants

Six of the seven rare species of turtles live here, the most ancient sharks, including whale, butterfly fish, sea bat, crocodiles and many other inhabitants of amazing shape and beauty. You can meet a huge flounder weighing from 200 kg and 2.5 m long. Dolphins, whales, killer whales grow their offspring near the reef. Many crustaceans build their homes here: lobsters, crabs, lobsters, shrimps. There are also deadly animals here, including blue-ringed octopuses.

Birds nest on the surface of stony formations: petrels, frigatebirds, terns, sea eagles and others, up to two hundred species. Of the plants, unfortunately, only 40 species are available.